1jd9
From Proteopedia
OCA (Talk | contribs)
(New page: 200px<br /><applet load="1jd9" size="450" color="white" frame="true" align="right" spinBox="true" caption="1jd9, resolution 2.5Å" /> '''CRYSTAL STRUCTURE ANA...)
Next diff →
Revision as of 16:00, 20 November 2007
|
CRYSTAL STRUCTURE ANALYSIS OF THE MUTANT K300Q OF PSEUDOALTEROMONAS HALOPLANCTIS ALPHA-AMYLASE
Overview
To further investigate the mechanism and function of allosteric activation, by chloride in some alpha-amylases, the structure of the bacterial, alpha-amylase from the psychrophilic micro-organism Pseudoalteromonas, haloplanktis in complex with nitrate has been solved at 2.1 A degrees, as, well as the structure of the mutants Lys300Gln (2.5 A degrees ) and, Lys300Arg (2.25 A degrees ). Nitrate binds strongly to alpha-amylase but, is a weak activator. Mutation of the critical chloride ligand Lys300 into, Gln results in a chloride-independent enzyme, whereas the mutation into, Arg mimics the binding site as is found in animal alpha-amylases with, however, a lower affinity for chloride. These structures reveal that the, triangular conformation of the chloride ligands and the nearly equatorial, coordination allow the perfect accommodation of planar trigonal monovalent, anions such as NO3-, explaining their unusual strong binding. It is also, shown that a localized negative charge such as that of Cl-, rather than a, delocalized charge as in the case of nitrate, is essential for maximal, activation. The chloride-free mutant Lys300Gln indicates that chloride is, not mandatory for the catalytic mechanism but strongly increases the, reactivity at the active site. Disappearance of the putative catalytic, water molecule in this weakly active mutant supports the view that, chloride helps to polarize the hydrolytic water molecule and enhances the, rate of the second step in the catalytic reaction.
About this Structure
1JD9 is a Single protein structure of sequence from Pseudoalteromonas haloplanktis with CA as ligand. Active as Alpha-amylase, with EC number 3.2.1.1 Full crystallographic information is available from OCA.
Reference
Structural basis of alpha-amylase activation by chloride., Aghajari N, Feller G, Gerday C, Haser R, Protein Sci. 2002 Jun;11(6):1435-41. PMID:12021442
Page seeded by OCA on Tue Nov 20 18:07:48 2007
